The synthesis of immunoglobulins has been studied in mouse myeloma cells cultured at reduced temperature. Under these conditions the rate of protein synthesis is reduced by approximately 75%. However, synthesis and secretion of immunoglobulins is reduced to a less extent, by about 40%. Secretion of immunoglobulins does not help in cells incubated at 27 degrees Centigrade, as previously reported for a different tissue culture line of myeloma cells. Increased synthesis of immunoglobulins at reduced temperatures has directly been demonstrated by pulse-labelling the cells and precipitating the immunoglobulin synthesized by means of specific antisera. The mechanism by which immunoglobulin mRNA is preferentially translated by membrane-bound polyribosomes has been investigated by studying the interaction of initiation complexes made of mRNA and single ribosomes with membranes obtained from mouse myeloma cells in tissue culture. mRNA has been isolated from free or membrane-bound polyribosomes and allowed to form initiation complexes with rabbit reticulocyte ribosomes. In a subsequent incubation, the binding of these complexes to membranes has been determined. No difference has yet been observed between initiation complexes formed with mRNA from free or membrane-bound polyribosomes. BIBLIOGRAPHIC REFERENCES: T.W. Borun, F. Gabrielli, K. Ajiro, A. Zweidler and C. Baglioni. Further evidence of transcriptional and translational control of histone messenger RNA during the HeLa S3 cell cycle. Cell, 4:59-68 (1975). Hickey, E., Weber, L.A., and Baglioni, C. Inhibition of initiation of protein synthesis by 7-methylguanosine-5' -monophosphate. Proc. Nat. Acad. Sci., 73:19-23 (1976).